Bending aluminium tube

Stuart Ord · Post by **Stuart Ord** » Sat Jan 30, 2010 9:39 am

I need to bend some 1 1/2" diameter aluminium thin wall (16SGW) tube for the induction of my Corby Starlet. Normal benders for thicker steel pipe won't work, apparently they just kink the inner radius under compression.

I'd prefer to do this at home but want to avoid expensive machinery purchase. The US web site pro-tools offer benders and even parts to make them but it still works out expensive. However it miight be my only option.

Can anyone offer a source of dies, expertise, pre-bent tube or services to do this? I suspect I can adapt the die for a normal pipe bender to the pulling action of the pro-tools type machine, so a die for 1 1/2" pipe with minimum centre line radius would be useful. If a service I'd prefer it in North Wales or Cheshire rather than having to post tube away for bending.

It was suggested I can bend aluminium by filling the tube with sand and bending on a standard pipe bender. Has anyone tried this?

Finally if I plunge in and buy an expensive bender, do you reckon it's a service much required by builders such that I might hire it out afterwards or offer to bend tube at a small charge to recoup some of the outlay? One problem is the dies are tube diameter and bend radius specific, and so providing a wide variety of options is not likely.

Thanks

Stuart

bertdeleporte · Post by **bertdeleporte** » Sat Jan 30, 2010 10:20 am

Hi Stuart,

I confirm, sand technique works, done myself on thin wall steel pipes. The important thing is to plug (cork, wood, plastic or rubber, whatever you have available) to keep the sand crammed inside the pipe. On steel pipes, heating is compulsory, on alu, I don't know, but cannot figure out how you could avoid it. The sand must be as dry as possible, the thinner the better, I used to pack it by hitting the tube for a few minutes and topping until complete filling.

Video available here (I did not see them, I have a Mac, but it might be usefull, download the files "cintrage au sable (remplissage)" and "cintrage au sable exécution" on the bottom part of the page)

http://tspeed.free.fr/deformtube.htm

In your case, can't you find elbows of short radius (1D, 2D) and make a welded construction? I belive the result would be of much better quality, I would go this way if I had to do it. By bending the pipe, you do not control the wall thickness on the circumference, the sand technique stretching the outter wall, but you never know ow far you are. Aluminium is tifficult to work hot, becaus you have no obvious clue of how hot you are (steel, copper become red, you "see" where you are; aluminium spakles a little bit, then melts...

).
Any piping company (offshore, shiprepair, industry) can offer you expertise and skill in the field, it is not DIY but will be of very high standard. Welding thin wall tubes with TIG asks to flow the pipe with argon during the welding and an very skilled worker, maybe it does not worth for you to spend hours, liters of argon and tens of tests pipes to reach that skill. Purchase the expertise, and get it done.

Bertrand

Stuart Ord · Post by **Stuart Ord** » Sat Jan 30, 2010 11:00 am

Hi Bertrand,

Thanks for your helpful and very quick reply! It's an interesting French website, that. The videos are very short and show them pouring sand into a but and then bending it round a circular mandrel with the aid of a blow torch. As you say, using heat is a bit hit and miss. I read that a good way to anneal alum before bending is to scrape soap onto is and heat until this turns black. That might help. Again a suitable mandrel is needed.

I like to DIY where possible but all the induction system is proving a problem. Originally I welded it up in stell exhaust pipe but it was very ugly and heavy. (Previously it had aluminium castings which were the wrong shape for its new cowl that I've fitted, hence the need for a new system.) I've tried welding aluminium with my MIG welder which sort of worked OK after following all the various advice, utube videos etc but it's like a sledgehammer and I can't make anything fine that way (hot box etc).

I've been trying out Durafix as an alternative but that's easy on simple jobs and seems to give good results, but it's hard on complex ones - the work gets hot everywhere very quickly and the brazing runs out of joints I've just completed! Do you know if the LAA considers Durafix any good?

There used to be a coded welder nearby who had nice TIG equipment at home who did parts for a previous aircraft but he's moved away. However I could find another I presume. Do you know where short radius bends can be obtained?

I keep wondering "will I be happy flying the aircraft if this isn't 100%?" and the answer of course is "no". However a motto I subscribe to is "anyone can fix a problem with enough money", so giving it all to someone else to do is a last resort.

Stuart

Bill McCarthy · Post by **Bill McCarthy** » Sat Jan 30, 2010 5:17 pm

Hows about trying one of those firms which make thin walled stainless steel exhaust pipes. You quite often see them almost formed into a figure of eight. I also note that on the "Luciole" the induction pipework is made out of composite material in order to keep weight down.

Stuart Ord · Post by **Stuart Ord** » Sun Jan 31, 2010 9:22 am

Thanks for all replies. I have one gentle bend to do, so I'll try the sand technique for that one. It will make specifying the "harder" bends easier to do. I think I will have to go to some professional benders and welders for the remainder. However I've e-mailed Richard Teverton for info on the Luciole - it's an interesting possibility.

As a further query, one further issue with the induction is that due to the inlet flanges on the opposing sides not being parallel, I can't use a solidly welded structure. My carb is behind the engine feeding mixture forwards over the top. I am planning the pipe from the carb splitting and bending to both sides until it is pointing towards the inlets, where it will bend down again and widening to the two, closely-spaced inlet holes. However as I say this pipe cannot be solid. Once made as separate parts to be bolted on independently, it needs a joint that can be added once the metal pipes are bolted into place. I have got some steel-reinforced rubber tube with 1.5" ID which slides onto the 1.5" OD ally tube whilst the bolts are done up, and then can be slid back over the gap and onto the mating tube to be secured by hose grips. However this tube is a bit ugly, and I'd expected to find suitable tube easily. However not so. I have searched all over for fuel proof rubber or polymer with 1.5" ID. I found some very expensive coated silicone but only available in >£100, 1m lengths. I did have rubber joiners for the Bing carbs on a Rotax 528 some years ago, so rubber seems to be OK. Can anyone suggest a source of a suitable joiner for this job?

Thanks

Stuart

cardiffrob · Post by **cardiffrob** » Sun Jan 31, 2010 10:06 am

Possibly worth a try...

Norman
Technical Tubes
Ferndown
Nr Wimborne
Dorset.
http://www.technicaltubes.com/innovations_industry.html

Not sure if he still works there or if it even exists nowadays but he did some fancy work for a Lancia engined MG Midget of mine a long time ago. They had some fancy tube bending stuff.

SAMCO make fancy hoses in silicone rubber for fuel and water lines. They probably also make the standard sizes also. http://www.samcosport.com/uk/index.asp

cardiffrob · Post by **cardiffrob** » Sun Jan 31, 2010 10:40 am

How about using a router to hollow out a thick piece of flat timber in the shape you need and then hammering a flat sheet over the resultant channel so that you form a half-piece that can then be welded to an identical one.

The other option is hydroforming. http://www.youtube.com/watch?v=I_Z3AIFSd60

This might also be a good lead? http://www.youtube.com/watch?v=v98jtIja ... re=related

Bill McCarthy · Post by **Bill McCarthy** » Sun Jan 31, 2010 11:33 am

The old metod of pipe bending with sand was to seal the sand in with pitch. You could also try melting some lead to fill the section of pipe. You need to leave plenty of "meat" either side of the bend for working with. Making tight bends in aluminium will break your heart though. With the best will in the world it is extremely difficult to avoid ovality and kinking even when working in stainless steel.

Stuart Ord · Post by **Stuart Ord** » Sun Jan 31, 2010 12:28 pm

More thanks!
Bill, I'm "pleased" others have grief at this, it's not just me......
Cardiffrob, the videas are very interesting. Hydroforming with my welding skills I'm sure will end in me being soaked! The other video by useful-tools.co.uk lead me to their web site. Curious how google hadn't found them in my many searches. Their tool only goes to 1 3/8" though and it still expensive (~£600 with die) - the pro-tools one does 1 1/2" and is cheaper. Pity. Samco looks a good lead - I'll try them on Monday. I'll give technical tubes a call too.
Rout a former and form some sheet for welding - sounds nice, but not with my MIG welder. Maybe I should just buy a good TIG welder and learn to use it...
Stuart

Stuart Ord · Post by **Stuart Ord** » Sun Jan 31, 2010 12:36 pm

Richard has just rung me - apparently a prototype Luciole had fibreglass induction, but they all use aluminium now.

Dave Holl · Post by **Dave Holl** » Sun Jan 31, 2010 11:33 pm

Why not cast?

bertdeleporte · Post by **bertdeleporte** » Mon Feb 01, 2010 11:36 am

Stuart Ord wrote:
Do you know if the LAA considers Durafix any good?
Do you know where short radius bends can be obtained?

I keep wondering "will I be happy flying the aircraft if this isn't 100%?"

Quick replies:
-No idea, check with local LAA inspector
-usually, pipe fitters mention radius of bend by ratio to diameter. For a 2'' pipe for instance, a 3D elbow will have a ID of tore (torus?) of 3 x D = 6''.
You now easily find 3D, 2D and 1D elbows for many diameters/materials. Even if the thickness is not perfectly matching, it is easy to weld thin pipe on thick elbow.

Keep wondering, it means you're still alive

I can read many others are very doubtful about the possibility to bend correctly alum pipe, plenty good other options proposed. If you go for composite, do not forget to fit a thermal barrier (silicon or fiber spacer) between cylinder head and manifold. Anyway, do not take any chance on induction manifold, if you want to preserve your engine of overheating/seizing due to abnormal leaning caused by air leak on the manifold. Pressure test looks for me compursary, water being always safer than air (liquid pouring vs gas expension in case of failure of the tested body).

If you need, I can have a look on what alum elbows I can source this side of the Channel (which is the good one, if you wonder also

)

Bertrand

Bill McCarthy · Post by **Bill McCarthy** » Mon Feb 01, 2010 4:05 pm

Welding aluminium is difficult enough, but to try to weld a cast elbow to drawn pipeware would be very tricky, and there is the added complication of bore matching the pieces.
Stuart - what engine are you fitting the induction system to ?